Theoretical Modeling and Numerical Simulation of Elliptical Capacitive Pressure Microsensor

Abstract

A capacitive pressure sensor consists of a movable diaphragm which causes change in capacitance for an applied pressure. In order to achieve high sensitivity, a thin diaphragm of large area is employed with a small separation gap. This introduces non-linearity, decreases the dynamic range and increases the size of the sensor. Thus, an optimum sensor design is necessary to balance these trade-offs. This paper presents theoretical modeling and numerical simulations on various performance parameters like diaphragm deflection, change in capacitance, mechanical and capacitive sensitivities and nonlinearity of a clamped and normal mode elliptical capacitive pressure sensor for 0 – 8 kPa operating pressure range. This analysis can form the basis for compact modelling (CM) of circular and elliptical capacitive pressure sensors for simulation with large scale circuits. In all the designs of elliptical and circular shape, the diaphragm thickness and separation gap are held constant at 7 µm and 1 µm respectively. The semi-major and semi-minor axes of the elliptical sensor have been varied from 100µm to 300 µm. We have taken into account the small deflection theory, Kirchhoff’s plate theory and pull–in phenomena while designing the model. To follow small deflection theory, the maximum diaphragm deflection is kept less than 1/10th of diaphragm thickness, and the maximum deflection is kept less than 1/4th of the separation gap to avoid pull-in.